Technical Field
The present invention relates to a technology for generating inspection image data for inspection of a defect or the like in a pattern formed on a surface of an inspection target by irradiating the inspection target with charged particles or electromagnetic waves.
In addition, the present invention relates to a technology for generating inspection image data for inspection of a defect or the like in a pattern formed on a surface of an inspection target by irradiating the inspection target with charged particles.
Background Art
Inspection systems are widely known in which a secondary charged particle which is obtained according to the properties of a surface of an inspection target such as a semiconductor wafer or the like is detected by a TDI (Time Delay Integration) sensor by irradiating the inspection target with charged particles or electromagnetic waves, whereby a pattern or the like which is formed on the surface of the inspection target is inspected by using image data generated based on the results of the detection (for example, International Publication No. 2002/001596, Japanese Unexamined Patent Publication No. 2007-48686, Japanese Unexamined Patent Publication No. 11-132975). In this inspection method, the irradiation of the inspection target with charged particles or electromagnetic waves is carried out while moving the movable stage to which the inspection target is held. The TDI sensor has imaging devices which are arranged in a stack in a predetermined number of stages in a vertical direction (which coincides with the moving direction of the movable stage). Amounts of secondary charged particles are integrated in the vertical direction in synchronism with the input of a transfer clock by using the time delay integration method, and an integrated detection amount of secondary charged particles is transferred in synchronism with the input of a transfer clock. A transfer clock is inputted into the TDI sensor at intervals of time which is necessary for the movable stage to move a distance corresponding to one pixel of the TDI sensor, that is, a distance in which a moving amount of an image projected on to the imaging device equals one pixel (this distance is determined by a magnification of an optical system) on the premise that the movable stage moves at a constant speed. According to this method, the amount of secondary charged particles is integrated by the predetermined number of stages, and therefore, when the inspection target is moved even at a high speed, a fast image picking up becomes possible.
However, in reality, it is difficult to move the movable stage at a constant speed at all times. This problem is caused by various reasons including the accuracy with which the system is built up, friction generated between the movable stage and the fixing member (for example, a guide rail), the accuracy with which the movable stage is controlled, and the like. In case there is generated a variation in the moving speed of the movable stage, an image that is picked up by the TDI sensor deviates to the front or rear in relation to an ideal state in which no variation is generated in the moving speed of the movable stage. The EO correction technology is developed to correct such a deviation. The EO correction technology is a technology in which an image that is projected on to the TDI sensor is corrected in relation to its position by using a deflector based on information on a difference between coordinates of a target position of the movable stage that is determined in advance and coordinates of a measured actual position (for example, Japanese Unexamined Patent Publication No. 2012-253007, Japanese Unexamined Patent Publication No. 2012-119694, Japanese Unexamined Patent Publication No. 2004-363085).
Additionally, in the inspection system, when a variation is generated in an emission current from an electron source, the luminance of an electron image changes, as a result of which, the luminance of an image that is outputted becomes uneven, leading to a reduction in inspection accuracy. To cope with this problem, a technology is known in which the emission current is controlled to stay at a set value through a feedback control by monitoring the emission current (for example, Japanese Unexamined Patent Publication No. 2006-324124).